1. Field of the Invention
The present invention relates to providing a user service in a wireless communication system, such as a universal mobile telecommunications system (UMTS), and more particularly, to providing a multimedia broadcast/multicast service (MBMS) in a plurality of cells by using one or more shared radio protocol entities.
2. Discussion of the Related Art
Referring to FIG. 1, illustrating a general UMTS network structure, the UMTS comprises a user equipment (UE) which is also referred to as a mobile terminal, a UMTS terrestrial radio access network (UTRAN), and a core network. The UTRAN comprises a plurality of radio network subsystems, each of which comprises one radio network controller (RNC) and at least one base station (or Node B) managed by the RNC. The Node B managed by the RNC receives uplink information transmitted from a physical layer of the UE and transmits downlink data to the UE, thereby serving as an access point for connecting the UE to the UTRAN. The RNC is responsible for allocation and management of radio resources and serves as an access point in connecting the Node B to the core network. An RNC managing radio resource for a specific UE is a serving RNC, and an RNC managing common resources for a plurality of UEs within one cell is a controlling RNC. A drift RNC is any RNC, other than the serving RNC, through which a UE communicates.
An interface between RNC and core network is the lu interface, an interface between serving RNC and drift RNC is the lur interface, and an interface between RNC and Node B is the lub interface. Each interface provides control information or data transfer service via a transport bearer. For instance, a bearer provided in the lub interface is an lub transport bearer, and the lub transport bearer provides control information and data transmission between RNC and Node B.
FIG. 2 illustrates the architecture of a radio interface protocol between one UE and the UTRAN. Referring to FIG. 2, a radio interface protocol vertically comprises a physical layer (Layer 1 or L1), a data link layer (Layer 2 or L2), and a network layer (Layer 3 or L3). The radio interface protocol horizontally comprises a user plane for providing data information and a control plane for providing control signals (signaling). The user plane carries user traffic for voice or Internet protocol (IP) packet transfer and the like. The control plane carries control information for the maintenance and management of interface or call within the network and the like. The protocol layers include first (L1), second (L2), and third (L3) layers, which are the three lower layers of the open system interconnection reference model.
The L1 layer provides an information transfer service to a higher layer using various radio transport technologies. The L1 layer is linked to a medium access control (MAC) layer of the higher layer via transport channels. Data is delivered between the MAC and physical layers via the transport channels.
The MAC layer provides reallocation services of MAC parameters for allocation and reallocation of radio resources. The MAC layer is connected to a radio link control (RLC) layer as a higher layer via logical channels. The logical channels are categorized, according to data type, as control channels or traffic channels. Generally, the control channels are used in transferring information of the control plane, and the traffic channels are used in transferring information of the user plane. The MAC layer comprises a MAC-b sublayer, a MAC-d sublayer, and a MAC-c/sh sublayer, categorized according to the type of transport channels being managed. The MAC-b sublayer manages a broadcast channel as a transport channel responsible for broadcasting system information. The MAC-c/sh layer manages common transport channels, which are shared with other UEs, such the forward access channel (FACH) and downlink shared channel (DSCH). The MAC-c/sh sublayer is located in the controlling RNC within UTRAN and manages the channels common with all the UEs within the cell. Hence, one MAC-c/sh sublayer exists in each cell, and one UE includes one MAC-c/sh sublayer. The MAC-d sublayer manages a dedicated channel (DCH) as a dedicated transport channel to a specific UE. Hence, the MAC-d layer of UTRAN is located in the serving RNC, and each UE also has one MAC-d sublayer.
To provide an MBMS service in accordance with the method of the present invention, an MBMS function is appended to the functions of the MAC-c/sh layer, thereby creating a MAC-c/sh/m layer. There is one MAC-c/sh/m layer per cell in the UTRAN and one MAC-c/sh/m layer per UE.
The radio link control (RLC) layer supports reliable data transfer and is operative in performing segmentation and concatenation of an RLC service data unit, which is delivered from a higher layer and adjusted in size to fit processing capacity in the RLC layer. A header is then appended to the adjusted RLC service data unit to be delivered to the MAC layer in the form of a protocol data unit. The RLC buffer exists in the RLC layer to store the RLC service data units or RLC protocol data units delivered from the higher layer.
A broadcast/multicast control (BMC) layer is located above the RLC layer, and schedules a cell broadcast message delivered from the core network, and is operative in broadcasting to UEs in a specific cell or cells.
A packet data convergence protocol (PDCP) layer is located above the RLC layer and is operative in efficiently transferring data, which is transferred via such a network protocol as lPv4 and lPv6, over a radio interface having a relatively small bandwidth. Thus, through a process known as header compression, the PDCP layer eliminates unnecessary control information utilized in a wire network, such that only information essential to the header is included for transfer, thereby enhancing the transmission efficiency of a radio section.
A radio resource control (RRC) layer, which is part of the L3 layer, is defined on the control plane only. Concerning the establishment, reconfiguration, and release of radio bearers, the RRC layer controls the transport and physical channels. A radio bearer is a service, provided by the second layer, for the data transfer between UE and UTRAN securing a certain QoS (quality of service). Radio bearer establishment, in general, defines the regulating characteristics of the protocol layers and channels needed to provide a specific service and respectively configures the respective parameters and operation methods. A UE is said to be in an RRC-connected mode when the RRC layers of the UE and the UTRAN are in communication with each other, to enable a communication of RRC messages, and is in the RRC-idle mode when there is no such communication.
An MBMS service provides a streaming or background service to a plurality of UEs using a downlink only MBMS radio bearer. In the UTRAN or a network, an MBMS service may utilize point-to-multipoint or point-to-point radio bearer services. The point-to-multipoint service generally represents transmitting data from a network to a plurality of UEs. The point-to-point service generally represents transmitting data from a network to a designated UE.
In the MBMS broadcast mode, multimedia data is transmitted to all UEs within a broadcast area, i.e., the domain where the broadcast service is available. In the MBMS multicast mode, multimedia data for a specific UE group is transmitted within a multicast area, i.e., the domain where the multicast service is available. MBMS service requires the support of two logical channels: an MBMS control channel (MCCH), which is a point-to-multi point downlink channel for transmitting MBMS control information to UEs, and an MBMS traffic channel (MTCH), which is a point-to-multi point downlink channel for transmitting MBMS data to UEs. One MCCH channel exists in each cell, and one MTCH channel exists for each specific MBMS within a specific cell. Both logical channels are mapped to a transport channel (FACH) and a secondary common control physical channel (S-CCPCH).
FIG. 3 illustrates MTCH protocol architecture according to a related art, in which an example RNC configuration has two Node Bs, with one managing three cells and another managing one cell. Each cell has separately configured radio bearer parameters for every PHY, RLC, and PDCP entity per MTCH channel per MBMS service in the UTRAN side. The same protocol entities are similarly established in the UE side (not shown).
In the related art, however, the network independently configures (and reconfigures) separate protocol entities for each cell. Hence, despite providing the same service, the protocol entities may be differently configured, whereby entity-associated parameter values are independently and separately set by the different protocol entities existing in the different cells, and the protocol entities providing the same service are independently managed and controlled. As a result, the UE needs to reconfigure new protocol parameters whenever it moves to another cell. Thus, there is an undesirable delay before a new radio bearer is established, during which time the UE has no radio bearer and thus receives no MBMS data. Therefore, data loss occurs when moving to a new cell. Moreover, the UE is unable to achieve soft combining gain, in which values from various cells are combined during a soft handover.